nx_blob_store_test.nx

nx_blob_store_test.nx -- smoke for nx_blob_store ST-1 MVP. Exercises: 1. Allocation + canary integrity + initial state 2. Put + get roundtrip on a known byte sequence 3. DEDUP: putting same bytes twice yields same hash + same entry count 4. Distinct bytes -> distinct hashes 5. has_blob positive + negative 6. SHA-256 determinism: same input across two stores produces same hash (content-addressing key property) 7. Bad-input gates (null bytes with len>0, negative len, null out_hash, null store, null hash, oversized buffer) 8. Capacity gate: filling beyond NX_BLOB_STORE_CAPACITY -> NX_BLOB_FULL 9. Tamper detection: stomp canary_post -> store invalidated; all subsequent ops refuse 10. nx_blob_hash_eq positive + negative + null gates 11. Empty-blob (len=0) round-trip